Which of the following are gauche conformers?
A)I and II
B)I and III
C)II and IV
D)II and III

Question

Which of the following are gauche conformers? 
A)I and II 
B)I and III 
C)II and IV 
D)II and III

Quizplus · Accepted Answer

In the given molecule, gauche conformers are those in which the largest groups (ethyl and methyl) are present in a staggered conformation with a dihedral angle of 60° or 300°. 
I - Both the ethyl and methyl groups are present in anti-conformation with a dihedral angle of 180°, hence not a gauche conformer. 
II - The ethyl group is present in a gauche conformation with the methyl group, dihedral angle= 60°, hence a gauche conformer.
III - Both the ethyl and methyl groups are present in anti-conformation with a dihedral angle of 180°, hence not a gauche conformer.
IV - The ethyl group is present in anti-conformation with the methyl group, dihedral angle= 180°, hence not a gauche conformer.

Which of the Following Are Gauche Conformers